Screening colonoscopy is seen as delivering among the best returns on public investment (Maciosek et al. Am J Prev Med 2006; 31:52-61, herein incorporated by reference in its entirety). Despite a growing body of data, only half of adults in the United States for whom a colonoscopy is recommended undergo the procedure (Cancer Prevention & Early Detection Facts and Figures 2006, American Cancer Society, herein incorporated by reference in its entirety). One of the major barriers to compliance is the unpleasantness of the preparation procedure (aka gastrointestinal lavage, colon gavage, colonoscopy prep, etc.)) (Harewood et al. Am J Gastroenterol 2002; 97: 3186-94, herein incorporated by reference in its entirety). Preparation of the colon for optical colonoscopy is important for an accurate and efficient exam. It is not surprising that poor preps result in higher miss rates for significant lesions (Froehlich et al. Gastrointest Endosc 2005; 61:378-84, herein incorporated by reference in its entirety), and are a major cause of lengthier, time-consuming exams (Rex et al. Am J Gastroenterol 2002; 97:1698-1700, herein incorporated by reference in its entirety).
There are a number of ways to cleanse the colon, each with advantages and disadvantages. The physician must balance the factors of patient safety, patient tolerability, and quality of the prep. For example, growing data on the risks of sodium phosphate preps has tempered enthusiasm for these types preps. Purgatives can be based on magnesium salts, sodium phosphate, or buffered saline solution with polyethylene glycol (PEG). Bisacodyl is sometimes added to the regimen to stimulate colonic motility. The downside of adding Bisacodyl to a cleansing regimen is that it may cause additional nausea and cramps. An overview of the current state of colonoscopy prep products is as follows:
Magnesium Salt Preparations
Magnesium salts, such as Magnesium Citrate are known to stimulate colonic mucosal ion secretion (Izzo et al. Br J. Pharmacol. 1994 September; 113(1):228-32, herein incorporated by reference in its entirety). Few gastroenterologists still use over-the-counter Magnesium Citrate solution as a prep. The only Magnesium-based solution designed for colonoscopy preparation is the LOSO PREP, a proprietary kit marketed by the EZ-EM Corporation. Magnesium Citrate is provided as a dry powder in a pre-measured pouch that is reconstituted with water or as a concentrated solution that is diluted before use. It is marketed with four 5 mg Bisacodyl tablets to take during the prep and a single 10 mg Bisacodyl suppository to use the morning of the procedure. Studies have examined its efficacy as bowel prep and show results similar to PEG-based preps with better tolerability (Delegge et al. Aliment Pharmacol Ther 2005; 21: 1491-1495, Rapier et al. Gastroenterology Nursing 2006; 29(4):305-308, herein incorporated by reference in their entireties). This has been studied in combination with an extremely low residue diet (NUTRA PREP, EZ-EM Corporation) with similar results. Electrolyte imbalances can occur if sufficient clear liquids are not consumed during the prep.
Sodium Phosphate Preparations
Sodium phosphate works as an osmotic agent and draws fluid into the colon, resulting in a purgative effect. Sodium Phosphate can be given as a solution (FLEET PHOSPHO-SODA EZ-PREP) or as tablets (VISICOL AND OSMOPREP). They are among the best tolerated colon preps from a patient's point of view (Hookey et al. Am J. Gastroenterol. 2004; 99(11):2217-22, Lichtenstein et al. Aliment Pharmacol Ther. 2007; 26(10):1361-1370, herein incorporated by reference in their entireties). It is critical for patients to drink sufficient quantities of clear liquids during these preps to ensure that the cathartic effect does not dehydrate them during the prep. The FLEET PHOSPHO-SODA PREP instructs patients to drink 24 ounces of fluid with the first dose of PHOSPHO-SODA, at least 24 ounces of clear liquids in between doses, and 24 ounces with the second dose. Patients who do not drink at least the required 2.1 liters of fluid during their prep are at significant risk of renal and electrolyte problems as a result of the prep.
During routine use of sodium phosphate preps, some of the phosphate is absorbed, and there is growing evidence that this may damage the kidney. Beginning in 2003, reports began to emerge about acute and chronic phosphate nephropathy in patients receiving phosphate-based preps, namely FLEETS PHOSPHO-SODA and VISICOL (Desmeules et al. NEJM. 200:349(10):1006-7, herein incorporated by reference in its entirety). The FDA now lists on their website more than thirty cases of renal injury associated with the use of phosphate salts for colon preparation. The FDA reports were associated with higher dosing regimens for phosphate preps (60 or more grams of sodium phosphate). No reports were received regarding the use of OSMOPREP®, which contains 48 grams of sodium phosphate. All regimens have now been brought below 60 grams of sodium phosphate. More recent studies in the Nephrology literature describe a relative risk for acute kidney injury at 1.5 to 3.6 times that of controls in those patients who have taken a phosphate-based colon prep (Markowitz et al. J Am Soc Nephrol 2005; 16:3389-96, herein incorporated by reference in its entirety). Patients who are at increased risk for this complication include people over the age of 57, and those with significant co-morbidity including hypertension, pre-existing CKD, and those patients taking either angiotensin converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARB). Because of the problems arising with sodium phosphate preps, training programs such as Mayo Clinic and University of Pennsylvania have relegated these preps to secondary status. Most recently, in December 2008, the FDA applied black-box warnings to VISICOL and OSMOPREP to highlight the risk for serious renal injury. Shortly after that, the C.B. Fleet Company voluntarily withdrew FLEETS PHOSPHO-SODA from the market due to its risk for renal injury when used as a colon prep.
Polyethylene Glycol (PEG) Preparations
Buffered saline solutions with PEG have been available for almost thirty years. While providing less risk to the patient with regard to fluid and electrolyte balance, the sheer volume of fluid to drink coupled with the poor palatability of some of these solutions have made them unpopular among the initiated. PEG based products are marketed under a variety of trade names (GO-LYTELY, COLYTE, NULYTELY, HALFLYTELY, GLYCOPREP, and MOVIPREP (see e.g., U.S. Pat. No. 7,169,381, herein incorporated by reference in its entirety)). COLYTE and GOLYTELY are the prototypical 4-liter colon gavage preps. The salty taste, nausea, and cramps cause the majority of patient complaints. NULYTELY was formulated as an improvement over GOLYTELY® with the deletion of Sulfate as an osmotic agent, increasing the PEG concentration to increase its osmotic effect, and the addition of flavor packs to improve palatability. The volume remains 4 liters. The latest iterations of PEG-based preps are HALFLYTELY and MOVIPREP. Both are 2-liter prep solutions. HALFLYTELY is marketed with two 5 mg Bisacodyl tablets to take during the prep to enhance colonic emptying. MOVIPREP does not require Bisacodyl but does require an additional liter of clear liquid be consumed during the prep. In general, the 2-liter PEG preps are better tolerated but not quite as cleansing as the 4 liter PEG preps.
One trend that is gaining popularity is the split-dosing schedule, wherein only half of the prep is taken the night before the procedure, and the remainder is taken early in the morning prior to the procedure. The split schedule improves tolerability for patients (Aoun et al. Gastrointest. Endosc. 2005; 62(2):213-8, herein incorporated by reference in its entirety). The diminished volume of any one dose reduces nausea and cramps. Ileal effluent (mucous, bile, and sloughed cells) may accumulate in the cecum and right colon overnight after completion of a prep. This material is often washed away by the morning dose in the split dose schedule. The split schedule requires that the patient get up early to take their morning dose 3 to 5 hours prior to their procedure. Some of the newer preps are designed as a split dose (FLEET'S PHOSPHO-SODA, VISICOL, OSMOPREP, and MOVIPREP). The 4-liter PEG preps can also be given as a split dose, usually 3 liters in the evening and 1 liter in the early morning.
Improving the diet prior to and during the prep may improve patient tolerance. There is some data indicating that the use of extremely low residue diets during the day of the prep (the day prior to the colonoscopy) instead of a clear liquid diet only may improve the tolerability of the regimen without diminishing the quality of colonic cleansing (Scott et al. Gastroenterol. Nurs. 2005; 28:133-139, herein incorporated by reference in its entirety). A pre-packaged low residue diet is marketed by E-Z-EM under the label NUTRA-PREP.
Typical gastrointestinal lavage formulations are described in US Pat. App. No. 2007/0098764, US Pat. App. No. 2007/0298008, Fordtran et al. Gastroenterology 1990: 98:11-16, Ernstoff et al. Gastroenterology 1983: 84:1512-6, Davis et al. Gastroenterology. 1980: 78:991-995, herein incorporated by reference in their entireties.
What are needed are improved systems and methods that improve patient tolerance and maintain safety and efficacy.